The disclosed technology relates to lubricants for internal combustion engines, particularly those for spark-ignited direct injection engines.
Modern engine designs are being developed to improve fuel economy without sacrificing performance or durability. Historically, gasoline was port-fuel injected (PFI), that is, injected through the air intake and entering the combustion chamber via the air intake valve. Gasoline direct injection (GDI) involves direct injection of gasoline into the combustion chamber.
In certain situations, the internal combustion engine may exhibit abnormal combustion. Abnormal combustion in a spark-initiated internal combustion engine may be understood as an uncontrolled explosion occurring in the combustion chamber as a result of ignition of combustible elements therein by a source other than the igniter.
Pre-ignition may be understood as an abnormal form of combustion resulting from ignition of the air-fuel mixture prior to ignition by the igniter. Anytime the air-fuel mixture in the combustion chamber is ignited prior to ignition by the igniter, such may be understood as pre-ignition. It will also be understood that ignition events generally increase in likelihood as the air-fuel ratio becomes leaner. As such, one approach to preventing pre-ignition events in GDI engines has been to intentionally inject additional fuel (i.e., to overfuel), thereby adjusting the air-fuel ratio to a richer mixture that is less favorable to pre-ignition events. This approach has successfully treated LSPI, but more current fuel efficiency and economy standards are causing engine manufacturers to adopt leaner air-fuel mixtures, which leads to the need for alternative approaches to preventing or reducing LSPI events.
Without being bound to a particular theory, traditionally, pre-ignition has occurred during high speed operation of an engine when a particular point within the combustion chamber of a cylinder may become hot enough during high speed operation of the engine to effectively function as a glow plug (e.g. overheated spark plug tip, overheated burr of metal) to provide a source of ignition which causes the air-fuel mixture to ignite before ignition by the igniter. Such pre-ignition may be more commonly referred to as hot-spot pre-ignition, and may be inhibited by simply locating the hot spot and eliminating it.
More recently, vehicle manufacturers have observed intermittent abnormal combustion in their production of turbocharged gasoline engines, particularly at low speeds and medium-to-high loads. More particularly, when operating the engine at speeds less than or equal to 3,000 rpm and under a load with a brake mean effective pressure (BMEP) of greater than or equal to 10 bars, a condition which may be referred to as low-speed pre-ignition (LSPI) may occur in a very random and stochastic fashion.
The disclosed technology provides a method for reducing, inhibiting, or even eliminating LSPI events in direct injection engines by operating the engines with a lubricant that contains a metal overbased detergent.